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| LOGO! retrofit brings more convenience and functionality to existing heating system | | Hot Times | Unsatisfied with the operation and convenience of his heating system, homeowner Klaus Hiller decided to do something about it. After being unable to find anything on the technical market, a friend advised him to extend his system with the LOGO! logic module. Now, with all his cares behind him, he is enjoying the snug warmth - LOGO! and the heating controller do all the "work behind the scenes".
Klaus Hiller lives happily with his family in Reicheltshofen in the beautiful Oberpfalz region. But he did have one problem or another with the cold time of the year. This was less to do with the weather than with his heating system, consisting of a conventional oil boiler plus a heating controller, a wood boiler with storage tank and a hot water tank. The heating controller responsible for the heating circuits and the control of the wood boiler was not optimally adjusted. There were deficits regarding the operation and convenience. But a complete replacement was out of the questions for Hiller. Thats when the idea of simply adding LOGO! 12/24 RC, an analog module AM2 PT100 and an extension module with four inputs and outputs to the heating system came up. Firstly, the task entailed the automatic switch-off of the fresh air blower of the wood boiler after burning the wood fuel, secondly, the supplying of the energy from the storage tank when requested by the oil boiler control and thirdly, the control of the hot water preparation during wood boiler operation. Hiller got support from a friend who helped him to design the control concept among other things. However, the mechanical engineer did the wiring, parameterization and commissioning himself. The programming is very simple to learn, he revealed. The graphic programming with simulation possibility is a great advantage. LOGO! is just fun to work with. The system has been working without any trouble since January 2006.
Switching off the fresh air blower
The first problem Hiller tackled with LOGO! was that the further operation of the fresh air blower after burning the fuel in the wood boiler led to an undesirable cooling in the combustion chamber if the blower was not switched off manually. LOGO! now does this job automatically. For this, the temperatures of the supply pipe to the storage tank and the return pipe to the wood boiler are measured by PT100 sensors. In normal heating operation the temperature difference is 6 to 12 K. At less than 2 K, no energy is transmitted to the storage tank, the wood fuel in the combustion chamber is burned and the fresh air blower is switched off. But there are two exceptional situations. The temperatures in the wood boiler and storage tank are approximately equal and the temperature difference lower than 2 K when stoking. Nevertheless the blower is switched on automatically for about 20 minutes. Then the water in the wood boiler is heated up so that the temperature difference is greater than 2 K.
The second exceptional situation occurs in the case of overheating. If the boiler water temperature exceeds a maximum value, the blower is switched off and the burn-off reduced. The heat development in the combustion chamber diminishes. The temperature difference can fall below 2 K. After the temperature of the boiler water has dropped accordingly, the blower is also switched back on at a temperature difference of less than 2 K because the fuel is not yet used up. LOGO! also recognizes this special case and does not switch off.
Energy from the storage tank
Depending on the weather, the heating controller of the oil boiler controls the supply temperature for the heating circuit. But whilst the oil burner is switched on/off as required in conventional heating systems, when heating with a wood boiler, the appropriate switching signal is sent to LOGO! and then a charge pump is started. This pumps heating water from the storage tank into the heating circuit. The charge pump is switched off on reaching the nominal temperature. This avoids unnecessary running times. The Hiller family heats exclusively with the wood boiler. The oil heating is only on when the family is away for longer than a day. Switching over is still manual at the moment. Im thinking of extending the control program, Klaus Hiller tells us about his plans for the future, so that it switches over to oil boiler operation when the energy in the storage tank has been used up. Ive already allowed for this in the wiring.
Preparing hot water in wood boiler operation
Hot water had previously been heated up by a hot water priority control. To enable fast heating of the hot water, the circulation pumps of the heating circuit were switched off. The advantages of this method was that the water in the storage tank had to be heated up to a temperature of at least 55°C first, before heating of the hot water could begin. The rooms could only be heated afterwards, after one or two hours. Klaus Hiller solved this annoyance by having the hot water heating controlled parallel to heating by LOGO!. For this, hot water is tapped from the supply by a separate pump and fed through the heat exchanger in the hot water tank. Im so glad I chose LOGO!. The convenient operation and the efficiency of the heating system have been increased considerably, a satisfied Klaus Hiller sums up.
GO! 1 / 2007 | |
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